Extensometer



June 1965 J. P. DE NICOLA ETAL smww EXTENSOMETER Filed Nov. 8, 1962United States Patent Ofiice dfififlfi? Patented June 22, 1965 3,190,007EXTENSQMETER Joseph P. De Nicola, North Quincy, and Wilharn P.

Hansen, In, Braintree, Mass., assignors to Instron Corporation, Canton,Mass, a corporation of Massachusetts Filed Nov. 8, 1962, Eer. No.236,225 Ciaims. (Cl. 33-447) This invention relates to extensometers,and more particularly to gas servo extensometers.

It is a primary object of the invention to provlde for accuratemeasurement of extension of a specimen even though the same ischaracterized by very high degrees of strain responsivity to stress. Itis a further object to provide such an extensometer in which any weightthat need be carried by the specimen owing to the extensometer isminimized to avoid as much as possible introduction of this extraneouscomplicating factor. It is yet another object to facilitate productionof a signal pursuant to specimen extension which may be easily given anydesired magnification, or if desired One degree of magnification duringone stage of strain and any other degree of magnification desired duringany other stage of strain.

Broadly, the extensometer of the invention features fixing a pair ofreference locations at axially spaced locations on a specimen, providinglocation-responsive valve actuating means, and providing in associationtherewith gas servo means tracking the valve actuating means, the gasservo means bearing signal producing means.

Other objects, advantages, and features will appear from the followingdescription of a preferred embodiment, taken in conjunction with theattached drawings thereof, in which:

FIG. 1 is a front elevational View, partially in section, of saidpreferred embodiment;

FIG. 2 is a side elevational view thereof;

FIG. 3 is a sectional view taken at 3-3 of FIG. 1; and

FIG. 4 is a sectional view taken at 44 of FIG. 1.

Referring now more particularly to the drawings, there is shown asupport it) upon which are fixed selectively at desired verticallocations by means of set screws 12 and 14 servo gas pressure housings16 and 18. Gas, suitably air, under pressure is supplied to each servothrough tubing 29, 20a, and 29b; and 22, 22a, and 22b, respectively. Theupper and lower servos have the same construction and mode of operation,so that only the upper is shown and described in detail. The said gasunder pressure enters axial passages 24 and 26 of vertically and axiallymovable slide 28, and thence through horizontal passages 30 and 32 tozones 34 and 36 on opposite sides of piston 38 moving in the cylindricalinner portion of housing 16, the piston 38 being axially movable withthe slide 28. Quad rings 46 and 41 provide sealing between piston 38 andslide 28, and housing 16. Nozzle 42 is supplied with gas pressure fromtube 20b and is in communication with passage 26. Vent 43 communicateswith zone 34.

Slide 28 is selectively fixed relative to mounting plates 44 and 46 bymeans of set screws 48 and 5t). Mounted on upper plate 44 is a positionsetting screw 52, while mounted on the lower plates is an LVDT 53 (orlinear variable differential transformer), for example of the typedisclosed in United States Patent No. 2,427,866, which is upwardlybiased by spring 54.

Fixed on plates 44 and 46 are flat spring steel reeds 56 carrying valvemembers 58 from which protrude feelers 60 extending underneath pins 62of light plastic collars 64 clamped around specimen S to define a linelocation around circular knife edge 66 and act as specimen-attachedelements.

In operation, the specimen S is held above and below by a pair of grips(not shown), and in this embodiment the lower grip is moved downwardlyrelative to the upper.

This has the effect of downwardly moving both clamp rings 64, inditfering amounts reflective of extension between the locations definedby the two circular lines 66. As each clamp ring moves downwardly itcarries with it its respective feeler 60. As each feeler 60 moves down,it bends reed 56 to lower valve member 58, increasing the gap betweenthe sameand nozzle 42. This has the effect of lowering pressure in thezone 36, causing pressure in zone 34 to drive down piston 38 until thegap between valve member 58 and nozzle 42 is once more that whichproduces equilibrium between pressures in zones 34 and 36. In thismanner mounting plates 44 and 46, which are fixed to slides 28, m0vedownwardly the same distances respectively as do the upper and lowerlines 66. The amount of extension, or difference between the amount ofmovement of the two lines 66, is reflected in LVDT 53, which produces anappropriate electrical signal.

Although in the embodiment shown no magnification either positive ornegative of the extension in the specimen is carried to thesignal-producing means, it will be apparent that the invention makespossible through simple link-ages making movement in thesignal-producing means less than or more than extension; and if desired,as for specimens which stretch slowly at first and then rapidly,producing a shift in the degree of magnification at a predeterminedpoint. It will also be apparent that another advantage of the inventionis that it permits easy adjustment to adapt for maximum use range withdiflferent gauge length between the lines 66 by virtue of set. screws12, and screw 52.

Other embodiments of the invention within the follow ing claims willoccur to those skilled in the art We claim:

1. An extensometer comprising a support, a pair of gas servos carried bysaid support, each of said servos including a mounting portion and anozzle, separate means responsive to movement of separate locations on aspecimen to produce a tendency to vary the size of a gas gap from eachof the respective nozzles, said servos being adapted to maintain aconstant gap whereby the respective mounting portions are moved tocorrespond with movement of said separate locations, and signallingmeans carried by said mounting portions for signalling relative movementtherebetween.

2. The extensometer of claim it in which said signalling means is alinear variable differential transformer.

3. An extensometer comprising a first gas servo with a first mountingportion and a first nozzle, 21 second gas servo with a second mountingportion and a second nozzle, each said mounting portion beingoperatively secured to the respective said nozzle for movement therewithin an extension direction, a first valve member movable relative to saidfirst nozzle in an extension direction and adapted to be moved in saiddirection responsive to movement of a location of a specimen in saiddirection, a second valve member movable relative to said second nozzlein an extension direction and adapted to be moved in said directionresponsive to movement of a second location of said specimen in saiddirection, and a signal producer cooperatively carried by said mountingportions for signalling the distance therebetween.

4. An extensometer for measuring relative change in position of twospaced points on a specimen as defined by first and second referencemembers coupled directly to said specimen at said two spaced points,said extensometer comprising a motion sensor adapted to be coupled toeach said reference member, each said motion sensor including structuredefining an orifice, a valve member positioned in front of and spacedfrom said orifice for controlling the flow of gas through said orifice,means for connecting said valve member to the associated referencemember for causing said valve member to move relative to said orifice inresponse to the motion of said associated reference member, conduitmeans for supplying gas for flow through said orifice, and meansresponsive to a change in gas fiow through said orifice produced by achange in the position of said valve member relative to said orifice toreposition said orifice defining structure to maintain a constant gapbetween said orifice and said valve member, and signaling means coupledbetween said two orifice defining structures for signaling relativemovement therebetween.

5. An extensometer for measuring relative change in position of twospace-d points on a specimen as defined by first and second referencemembers coupled directly to said specimen at said two spaced points,said extensometer comprising a motion sensor adapted to be coupled toeach said reference member, each said motion sensor including a nozzle,a nozzle mounting portion, a valve member positioned in front of andspaced from said nozzle for controlling the fioW of gas through saidnozzle, means for supporting said valve member on said nozzle mountingportion, means for connecting said valve member to the associatedreference member for causing said valve memher to move relative to saidnozzle in response to the motion of said associated reference member,conduit means for supplying gas for flow through said nozzle, and meansresponsive to a change in gas flow through said nozzle produced by achange in the position of said valve member relative to saidnozzle toreposition said nozzle to maintain a constant gap between said nozzleand said valve member, ouptut means coupled between said mountingportions for sensing the change in position of said mounting portionsand producing output signals indicative of such position change, andmeans to adjust the position of one mounting portion relative to theother mounting portion.

References Cited by the Examiner UNITED STATES PATENTS 1,946,924 2/34Allen et al 33-148 X 2,455,285 11/48 Versaw 33 2,669,246 2/54 Segerstad33147 X 2,876,551 3/59 Bowlby 33-447 2,982,124 5/61 Knobel 73.73,065,415 11/62 Slarnar 33-147 X ISAAC LISANN, Primary Examiner.

1. AN EXTENSOMETER COMPRISING A SUPPORT, A PAIR OF GAS SERVOS CARRIED BYSAID SUPPORT, EACH OF SAID SERVOS INCLUDING A MOUNTING PORTION AND ANOZZLE, SEPARATE MEANS RESPONSIVE TO MOVEMENT OF SEPARATE LOCATIONS ON ASPECIMEN TO PRODUCE A TENDENCY TO VARY THE SIZE OF A GAS GAP FROM EACHOF THE RESPECTIVE NOZZLES, SAID SERVOS BEING ADAPTED TO MAINTAIN ACONSTANT GAP WHEREBY THE RESPECTIVE MOUNTING PORTIONS ARE MOVED TOCORRESPOND WITH MOVEMENT OF SAID SEPARATE LOCATIONS AND SIGNALLING MEANSCARRIED BY SAID MOUNTING PORTIONS FOR SIGNALLING RELATIVE MOVEMENTTHEREBETWEEN.